Wireless communication systems are widely deployed to provide various types of communication such as voice and data. These systems may be based on code division multiple access (CDMA), time division multiple access (TDMA), or some other modulation techniques. A CDMA system provides certain advantages over other types of systems, including increased system capacity.
A CDMA system may be designed to support one or more CDMA standards such as (1) the “TIA/EIA-95-B Mobile Station-Base Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular System” (the IS-95 standard), (2) the standard offered by a consortium named “3rd Generation Partnership Project” (3GPP) and embodied in a set of documents including Document Nos. 3G TS 25.211, 3G TS 25.212, 3G TS 25.213, and 3G TS 25.214 (the W-CDMA standard), (3) the standard offered by a consortium named “3rd Generation Partnership Project 2” (3GPP2) and embodied in a set of documents including “C.S0002-A Physical Layer Standard for cdma2000 Spread Spectrum Systems,” the “C.S0005-A Upper Layer (Layer 3) Signaling Standard for cdma2000 Spread Spectrum Systems,” and the “C.S0024 cdma2000 High Rate Packet Data Air Interface Specification” (the cdma2000 standard), and (4) some other standards.
Pseudorandom noise (PN) sequences are commonly used in CDMA systems for spreading transmitted data, including transmitted pilot signals. Inherent in the design of direct sequence CDMA systems is the requirement that a receiver must align its PN sequences to those of a base station. In some systems, such as IS-95 and cdma2000, base stations are differentiated by transmitting a common PN sequence with a unique offset. Other systems, such as those defined by the W-CDMA standard, differentiate base stations using a unique PN code for each. The process by which a mobile station acquires the pilot signals of neighboring base stations in known as searching.
A mobile station may be in communication with a network of base stations, some of which may be transmitting on different frequencies, and some of which may use alternate air interface schemes. An example may include a system using equipment conforming to one or more of the above named standards. In such a scenario, occasional searches across multiple frequencies and systems may be needed for the mobile station to keep track of the best quality cell. Tracking and communicating with the best quality cells can result in better signal transmission and reception, often at reduced transmission power levels by both the base station and the subscriber unit. This, in turn, increases the capacity of the CDMA system (either in terms of support for an increased number of users, or higher transmission rates, or both).
One method for supporting multi-frequency, multi-system search is to deploy multiple parallel searches to support the various frequencies and systems. This solution may prove costly in terms of the hardware required to support it.
Another solution is to time-share a single searcher, for use on a variety of frequencies and systems. One problem with this second solution is that an ongoing search can be interrupted by a new search request scheduled on a different frequency or system. Often this is handled by aborting the search in progress to make resources available for the new search. This is an inefficient use of the available resources. Another problem can arise when the search resources are only available for a limited time to search alternate frequencies and/or systems. In some cases, the limited time may not be sufficient to complete the alternate search. There is therefore a need in the art for a searcher that can perform segments of one or more search tasks, ultimately combining the results to generate one or more completed search tasks.